The present invention relates to a dry toner, to processes for the production of the dry toner, to the use of the dry toner, to a toner cartridge and to a printed product.
In recent years full color printers or color copiers, especially for the development of digital electrostatic images, have attracted much attention and are continuing to make advances.
The production of full color pictures by the principle of full color electrophotography is normally achieved by reproducing the colors with colored toners of the three primary colors yellow, magenta and cyan or with four-colored toners which additionally contain a black toner.
Electrophotography generally includes the production of a latent electrostatic image on a photoreceiver using a photoconductive substance, the development of the latent image with toner and, after the toner image has been transferred to paper etc., fixation of the toner image by the use of heat, pressure and solvent vaporization.
Color copying by employment of electrophotography is performed by multiple exposure of an original through a color filter and developing each electrostatic latent image with a suitable color toner, i.e. generally with yellow, magenta and cyan color toners in order to produce a color image consisting of a plurality of superimposed toner images.
In order to represent lustrous color impressions, it has hitherto been necessary to resort to toners having the aforementioned fundamental colors, yellow, cyan, magenta and black, but in such cases the problem has always been that the angle-dependent impressions of color, brightness and brilliance as well as the high luster of metallic surfaces could not, or only inadequately, be represented using such color combinations.
There has been no lack of attempts to produce color toners that could compensate for these deficiencies.
Patent applications JP 63100468 A, JP 62127754 A and JP 62127753 A disclose toner compositions with which metallic effects are reported to be simulated by using dark titanium oxide layers on platelet-type substrates with platelet-type purine derivatives or fish scales.
The patent applications JP 62100770 A and JP 62100771 A describe a silver or gold colored toner for electrophotography that is based on inorganic support materials coated with titanium oxide and/or iron oxide.
The toners described in the above-cited patent applications, however, to their detriment do not adequately approximate the properties of metal effect pigments in terms of color impression and covering power.
In U.S. Pat. No. 6,376,147 B1 a liquid toner composition is described in which metal effect pigments are used. The use of solvents in the toner composition is especially unfavorable from the standpoint of environmental friendliness and occupational safety. Another drawback is the fact that only a very limited number of printers are available for the use of liquid toner formulations. These printers must also be secured against the hazard of explosion because of the use of solvents in the toner compositions.
WO 2005/076086 A1 discloses a metallic color toner containing metal pigments having an organic coating. The organic coating used is an aliphatic acid, an acid amide, an acid salt, olefinic material, natural wax, synthetic wax, a polymer, or a combination of these. Optionally, an additional silicate, titanate, or aluminate layer may be applied to the metal pigment. A serious disadvantage is the fact that when stearic acid is used, i.e. an aliphatic acid, the toner material undergoes plasticization. Another disadvantage is that no prints with a lustrous and brilliant metallic appearance can be produced with this metallic toner.
In view of the above-listed disadvantages of toners, a need exists for a toner composition that is substantially dry, i.e. low in solvent, and, when used in electrophotographic printing processes, yields brilliant and angle-dependent reflecting prints of high color intensity.